1. Field of the Invention
The present invention relates to a frequency control method and an oscillator in an electronic device, and more particularly, to a method and apparatus of making frequency jitter to lower EMI (Electromagnetic Interference).
2. Description of the Prior Art
Currently, most consumer electronic devices adopt switching power supplies as power supplies. The switching power supply controls energy storage and discharge of an inductor by switching a power switch to provide power fulfilling specification requirements. If the switching of the power switch is always maintained at a specific frequency, an electromagnetic wave with the same specific frequency tends to radiate through connections among electronic devices, leading to an EMI problem.
One way to solve the EMI problem is to make the switching frequency of the power switch jitter around a specific frequency, i.e., frequency jittering. U.S. Pat. Nos. 6,107,851, 6,249,876 and 7,391,628 provide different methods of frequency jittering. However, these prior art methods all require considerable chip areas.